The present invention concerns a magnetic bubble memory element, and more particularly it concerns the construction of a conductor loop for generating or dividing magnetic bubbles wherein even when generation or division of magnetic bubbles is repeated for a long time, such erroneous operations as the excessive generation of magnetic bubbles and the extinction of necessary magnetic bubbles can be prevented. Widespread use has hitherto been made to magnetic bubble memory elements of so-called pulse current type wherein pulse current is passed through a hair pin shaped conductor loop to generate or divide the magnetic bubbles.
FIG. 1 shows the main part of one example of the conductor pattern for generating magnetic bubbles which is designed for use in the pulse current type magnetic bubble memory. In the figure, reference numeral 1 designates pattern layer segments constituting a magnetic bubble propagation circuit, the propagation circuit segment 1 being a fine pattern of a soft ferromagnetic thin film such as made from permalloy. Reference numeral 2 designates a hair pin shaped conductor loop of a conductor pattern layer through which is passed working current, the conductor loop 2 being a non-magnetic, conductive thin film.
Ordinarily, the magnetic bubble propagation circuit pattern layer and the conductor pattern layer are laminated in the direction vertical to the sheet of drawing, with a hair pin portion 2a of the conductor loop positioned in such a way that it crosses the propagation circuit segment 1. A rotating magnetic field 3 (H.sub.R) which is applied to the pattern layers from outside rotates in a counterclockwise direction so as to propagate the magnetic bubbles from right to left (in the direction of the arrow p). A bias magnetic field 4 (H.sub.B) acts from rear to front of the sheet of drawing in order to stably keep the magnetic bubbles on the propagation circuit.
In the magnetic bubble memory element thus constructed, the magnetic bubbles are generated in the following manner. When the rotating magnetic field 3 (H.sub.R) turns to the vicinity of 0.degree., the working pulse current I is supplied to the conductor loop 2. Then, the pulse current I flows in the direction to weaken the bias magnetic field 4 (H.sub.B) so that magnetic bubbles B.sub.1 are generated within the loop of the hair pin portion 2a of the conductor loop. The magnetic bubbles B.sub.1 propagate over the propagation circuit from right to left (in the direction of the arrow p) in accordance with the rotation of the rotating magnetic field 3 (H.sub.R).
With the conventional magnetic bubble memory element as described above, however, such erroneous operations as the excessive generation of magnetic bubbles and the extinction of necessary magnetic bubbles are encountered in the repeating generation for a long time of the magnetic bubbles by supplying pulse current I to the conductor loop 2. That is to say, the magnetic bubbles are generated by passing a working pulse current I of 200 mA to 400 mA amplitude and 100 ns to 300 ns pulse width through the conductor loop 2. When such a pulse current I flows through the hair pin portion 2a of the conductor loop 2, there is generated Joule heat. Particularly the pulse current I of that amplitude raises the current density J at the hair pin 2a of the conductor loop 2 to an extremely high value of 10.sup.7 A/cm.sup.2, thereby accelerating the heat generation at the conductor loop 2 by Joule heat, and raising the temperature in the conductor loop 2 to very high values. As will be seen from the temperature distribution shown in FIG. 2, the temperature at the tip of the hair pin part 2a rises to about 90.degree. C. whereas the temperature is about 10.degree. C. at the root adjacent to the hair pin 2a.
Such an abnormally high and localized temperature at the tip of the hair pin portion 2a will hinder normal magnetic bubble generation and propagation, and will cause the erroneous operations in which magnetic bubbles are generated excessively and/or magnetic bubbles once generated are forced to disappear.